ANCYLUS RIVULARIS, Say. 



PLATE 1. FIG. 1. 

 A. testa ovata, sublata, subelevata, apice obtuso. 



SYNONYMS AND REFERENCES. 

 A. RIVULARIS, SAY. Journ. Acad. Nat. Sci., I. 125. 



DESCRIPTION. 



ANIMAL plumbeois, minutely dotted with 

 whitish: a central yellowish longitudinal line 

 upon the head: foot emarginate in front, extend- 

 ing to the mouth, where it is very thin. 



SHELL delicate, moderately elevated; sides 

 slightly convex, diverging anteriorly: posterior 

 and dextral slopes concave, anterior slope con- 

 vex, and sinistral one nearly rectilinear: apex 

 subacute, projecting, one-third of the shell 

 posterior to it. 



COLOR light brown; nacre, in large individuals, 

 white. 



DIMENSIONS. Long. 5, lat. 3.5, elev. 2 milli- 

 metres. 



GEOGRAPHICAL DISTRIBUTION. The Delaware 

 and Susquehanna. 



